The invention pertains to electromagnetically activated pressure modulation valves, in particular, control valves containing two independently actuated solenoids.
The control of fluid flow utilizing electromagnetically actuatable solenoid valves is well known and has been generally applied to control the flow of viscous fluids in hydraulic systems, such as power steering systems or in refrigeration systems, as well as, in pneumatic systems such as automatic air-brake, welding and exhaust gas purification systems for emissions control of automobile emissions.
In nearly all of the uses of electromagnetic flow control valves, a valve member is required to form a fluid tight, i.e., pressure tight seal. The word fluid is used in its generic sense including both liquids and gases.
Illustrative of a first class of electromechanical solenoid valves is that class of valves containing a single solenoid. These valves provide essentially an on-off type of fluid control and are typically inserted directly within a fluid carrying conduit. When actuated they either permit or inhibit fluid flow.
Illustrative of this type of valve is Van Domelen's solenoid actuated flow valve as recited in U.S. Pat. No. 3,125,321, issued Mar. 17, 1964. Brunning in U.S. Pat. No. 1,557,192, issued Oct. 13, 1925, illustrates the use of a single solenoid valve to control the flow of water within a refrigeration system; while McLead in U.S. Pat. No. 2,300,263 issued on Oct. 27, 1942, to control an air piston within a welding apparatus.
Furthermore, it has been realized that electromagnetic valves can and do more than merely restrict or enhance the flow of fluid within a simple conduit. Consider a second class of fluid control valves wherein the class is characterized by valves containing two solenoids. This class of valves can be utilized as amplification devices wherein a low pressure source is used to control and modulate the application of fluid under a different and higher pressure to fluid responsive mechanism. The use of a bi-valve as an amplication device in a pressurized hydraulic system is disclosed by Pearson in U.S. Pat. No. 3,565,111 which issued Feb. 23, 1971. Franz on the other hand utilizes two solenoids as shown in U.S. Pat. No. 3,340,773, issued Sept. 12, 1967, to control two valves in order to pressurize either side of a power diaphragm, which is integral with the valve body, to regulate the magnitude of the longitudinal movement of the piston. Activation of either solenoid causes a change in the pressure differential across the diaphragm.
To achieve efficient control of pneumatic pressure responsive actuators, such as an EGR valve (exhaust gas recirculation, part of an automotive emissions control system) requires a low cost control valve capable of modulating the applied vacuum at a high flow rate without severely bleeding the available engine vacuum.
To achieve precise position control of a pneumatic actuator within an emissions control system further requires a control valve characterized by a fast opening and closing time. A rapid and responsive control valve enables the application of electronic control technique such as pulse width modulation to control pressure communication and correspondingly yields a fine stepwise movement capability of the pneumatic actuator.
An object of the invention is a control valve capable of operating as a vacuum modulator or as a pressure modulator to provide precise control of a pneumatic actuator and having rapid response times.
Another object of the invention is a pneumatic actuator responsive to continuous electric current and pulsed current control methods.
The advantages of the present invention are that a precise low cost pneumatic modulator is achieved. In particular, when the control valve is used as a vacuum modulator, to control an actuator such as an EGR (exhaust gas recirculation) valve, control is achieved without a continuous air bleed from the vacuum source. In addition, minute actuator repositioning is possible because of the quick response times (6 millisecond opening, 2 millisecond closing) achieved by the present design. Furthermore, testing has shown that the modulator does not exhibit any significant changes in performance over a wide temperature range from (-40.degree. F. to +250.degree. F.) as compared to performance conducted in an ambient environment. In addition, to enhance the speed of response of the valve, the maximum developed magnetic forces exerted upon a slideable valve are mechanically controlled.